David Cameron is falling over himself to buddy up with Barack Obama, and is likely to support him on foreign policy. Photograph: Christopher Furlong/Getty Images

Picture the scene: it's 3am and the phone rings in No 10. A bleary-eyed David Cameron finds Barack Obama on the end of the line. An attack on the Iranian nuclear reactor in Bushehr is imminent and "we need Britain with us on this", says Obama. "We need your base in Diego Garcia, we need logistical support in the Persian Gulf, and above all, we need you to stand with us in the UN."

A horrible scenario – but not outside the realms of possibility. Especially if the missile is an Israeli one. And it's one worth considering, because as public attention focuses on the clear rift between the Conservatives and the Lib Dems on the EU, an equally yawning chasm exists in another major and more pressing policy area: the Middle East.

So what does Cameron do next? Does he ask Obama to hold while he calls Nick Clegg? And what if Clegg says no or that he has to ask his party first?

Even if the Conservatives had won a majority in the elections, their Middle East policy would have been likely to be a muddled affair. As far as Israel-Palestine goes, "We're just not that interested," a party activist cheerfully admitted just before the election. One Middle East diplomat predicted succinctly that any Tory policy would be "opportunistic" at best.

And this opportunism will be guided on every aspect of Middle East policy by the transatlantic alliance. Hague may say that Britain will have a "solid, not slavish" attitude towards America – he might as well be shrieking: "We're no poodles!" – but he is a committed Atlanticist and Cameron is falling over himself to buddy up with Obama. The feeling seems mutual – the US president was quick to congratulate the new prime minister, apparently delighted to say goodbye to the lugubrious Gordon Brown.

So Britain will talk tough on West Bank settlements if Washington wants it to, it will keep its 9,000 troops in Afghanistan as long as Washington needs it to and it will use its role in the EU 3+3 to lobby for tougher sanctions on Tehran. Most significantly, Hague has always refused to rule out supporting any future military strike on Iran, whether Israeli or American.

So while the two parties will have time to work out their issues on Europe – after all, EU affairs tend to grind forward with monolithic slowness – a foreign crisis further away will give them much less time to reconcile their differences. The reaction of both parties will be guided by ideological instinct.

There is no mention of any foreign policy at all beyond Europe in the coalition agreements; and no clarity on how Clegg and Cameron will deal with a foreign crisis together.

The Tory leadership on foreign and military policy is Cameron/Hague/Fox and you can bet your bottom dollar that if that dreaded 3am call comes, they will be in favour of saying an immediate "yes" to Obama.

You can also bet your last euro that the ensuing Lib Dem rift would paralyse Britain's foreign policy – if not destroy the government.

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